The specific or practical details; the heart of a matter.
The actual, basic facts, elements, issues, etc.
Nitty-gritty is slang for the basic facts, key details or most practical aspects.
Knowing the date, time and place of a party are an example of the nitty-gritty of planning a party.
Origin of nitty-gritty
Uncertain, said to have been used at first by black jazz musicians, perhaps ultimately from reduplication nit and grits (finely ground corn), from Old English grytt, grytta (“coarse meal").